Modulation

When sounds are added together, they can create new textures. However, we can also use one sound to control the properties of another, creating patterns or rhythms.

What Is Modulation?

Modulation means ‘to change or adjust’. The term is often used in traditional music to describe a change in musical key or to describe tremolo and vibrato. But in reality, anything can be modulated. For example: when I open a bottle of tomato sauce, my hand modulates the lid from closed to open.

The technical process of analogue soundwave modulation involves two signals:

Carrier signal – the main signal that is affected by the process.

Modulating signal – the signal that affects and changes the carrier signal.

In the following examples, we will observe how the modulating signal affects the carrier signal.

Amplitude Modulation

Frequency Modulation (FM)

In Frequency Modulation, the frequency of an original carrier signal is affected. In this case, the modulating signal does not affect the loudness (or amplitude of the sound), this remains constant. But it does change the frequency (number of waves per second) of the original signal.

Frequency Modulation

This sound begins as a simple tone, over time more Frequency Modulation is applied.

LFO (Low Frequency Oscillator)

Not anything to do with aliens, I’m afraid. An LFO is a Low FrequencyOscillator, an oscillator (a back and forth wave) that moves very slowly (at a low frequency). LFOs are modulating signals – they transform other sounds. They are very common in many synthesisers and used frequently in lots of different styles of music. They can be used to affect any number of parameters: frequency, amplitude or rate of change.

LFO Controls a Filter

Fact

Dubstep is a style of music that makes significant use of modulation. The ‘wobble’, that is the most recognisable feature of Dubstep, is caused by low frequency modulation of a filter, affecting the main synthesiser tone.